1. Field of the Invention
The present invention relates to an oil level equalizing system for a plurality of low-pressure shell-type compressors arranged in parallel.
2. Description of Related Art
Japanese Laid-Open Utility Model Publication (unexamined) No. 4-19675 discloses an oil level equalizing system for a plurality of low-pressure shell-type compressors arranged in parallel.
This oil level equalizing system will be explained hereinafter with reference to the attached drawings. FIG. 19 depicts a refrigerating cycle of an air-conditioning equipment employing the conventional oil level equalizing system for the plurality of compressors. FIG. 20 is a detailed view of a portion denoted by A in FIG. 19.
In FIGS. 19 and 20, an outdoor unit 1 of the air-conditioning equipment comprises a plurality of low-pressure shell-type compressors 2a, 2b, 2c, a four-way valve 3 for switching the flowing direction of a refrigerant in accordance with a cooling operation and a heating operation, an outdoor heat exchanger 4 which serves as a condenser during the cooling operation and as an evaporator during the heating operation, and an outdoor expansion valve 5 which does not reduce the pressure during the cooling operation but serves as a pressure reduction unit during the heating operation. An indoor unit 6a, 6b or 6c comprises an indoor expansion valve 7a, 7b or 7c which does not reduce the pressure during the heating operation but serves as a pressure reduction unit during the cooling operation, and an indoor heat exchanger 8a, 8b or 8c which serves as an evaporator during the cooling operation and as a condenser during the heating operation. Further, the outdoor unit 1 is connected with the indoor units 6a, 6b, 6c thereby constituting a looped refrigerant circuit.
Reference numeral 9 designates a suction line which communicates with the suction side of the compressors 2a, 2b, 2c, and reference numerals 10a and 10b designate branch portions of the suction line 9.
The compressors 2a, 2b, 2c are connected at respective positions adjacent to the normal oil level within the shell with an oil level equalizing line 11 via connecting lines 12a, 12b, 12c.
An oil level controlling method for each compressor in the air conditioning equipment of the above-described construction will be explained hereinafter.
When the oil level rises due to an increase in the oil quantity within the shell of any one of the compressors 2a, 2b, 2c, the pressure at the connecting portion of the corresponding connecting line 12a, 12b or 12c increases. In contrast, when the oil level lowers due to a reduction in the oil quantity within the shell of any one of the compressors 2a, 2b, 2c, the pressure at the connecting portion of the corresponding connecting line 12a, 12b or 12c decreases.
Accordingly, for example, when the oil quantity within the compressor 2a decreases due to oil foaming or the like at the time of starting, the oil level within the compressor 2a lowers, so that the pressure at the connecting portion of the connecting line 12a of the compressor 2a lowers below the pressures at the connecting portions of the connecting lines 12b, 12c of the compressors 2b, 2c. Therefore, the oils within the shells of the compressors 2b, 2c transfer into the shell of the compressor 2a through an oil level equalizing line 11 to prevent shortage of the oil quantity within the compressor 2a. In this way, when the respective compressors 2a, 2b, 2c have the same capacities and the pressures within their respective shells are the same, it becomes possible to adequately control the oil quantities within the respective compressors 2a, 2b, 2c.
However, when one or more compressors having different capacities or variable capacities are included among the plurality of compressors 2a, 2b, 2c, since the respective compressors 2a, 2b, 2c are of the low-pressure shell-type, the pressures within the shells of the compressors of the high capacity type lower and the pressures within the shells of the compressors of the low capacity type rise.
Accordingly, for example, when the compressor 2a has a smaller capacity than those of the compressors 2b, 2c, the pressure within the shell of the compressor 2a becomes higher than those within the shells of the compressors 2b, 2c, and the pressure at the connecting portion of the connecting line 12a of the compressor 2a becomes higher than those at the connecting portions of the connecting lines 12b, 12c of the compressors 2b, 2c, so that the oil within the shell of the compressor 2a transfers into the shells of the compressors 2b, 2c through the oil level equalizing line 11 to decrease the oil quantity of the compressor 2a.
At this moment, the oil stirred by rotary elements or the oil dropping from the compressor drifts in mist state within the shell of the compressor 2a, and the oil in the mist state also transfers into the compressors 2b, 2c together with the refrigerant.
Accordingly, even when the oil level within the compressor 2a lowers below a connecting position of the connecting line 12a, the oil quantity continues to decrease and becomes short before long to consequently damage the compressor 2a.
In this way, when the plurality of compressors having different capacities are used, there arises the problem that the oil quantity within the low capacity compressor becomes insufficient.
In order to solve that problem, it may be proposed that all the compressors are stopped and supplied with the oil for equalizing the oil levels at predetermined time intervals. In this case, however, since the time may be usually set to several minutes to several tens of minutes, the operation is frequently turned ON and OFF to make the system unstable, resulting in a reduction in efficiency and reliability of the system.